The aims of this project are to define alloantisera directed against the cell surface antigenic specificities of murine lymphocytes and tumor cells. The study is based on the finding of an extensive antigenic variation in the surface of lymphocytes in the mouse, and that this variation can be used to identify different functional lymphocyte subpopulations. Thus the anti-lymphocyte alloantisera are extremely useful in identifying and defining interacting lymphocyte populations, and as probes to define previously unrecognized cell types. The aims are therefore: (1) to identify new lymphocyte alloantigens; (2) to characterize, genetically, new antisera and to further characterize previously described antisera, especially anti-Ly-6 and Ly-7; (3) to describe new methods of anti-Ly serum production which should lead to the production of high titered antisera of greater specificity and which includes the production of B cell "hybridomas"; (4) to define new methods of testing antisera, especially methods which can detect small numbers of cells reacting with antisera; (5) to produce congenic lines for new specificities including Ly-4, Ly-6 and Ly-7; (6) to determine the cells reacting with the antisera, both by using special techniques to define T and B cells and subpopulations thereof and by using the appropriate functional assays to define these subpopulations; (7) to test various lymphoid tumors with antisera as part of the characterization of both antisera and tumors. The studies should provide extensive information on the lymphocyte surface; on functional subpopulations and on the tissue of origin, type, and classification of many tumors, which, in turn, may indicate means of manipulating the immune response in vivo.